diff --git a/enabler/src/de/schildbach/pte/AbstractHafasProvider.java b/enabler/src/de/schildbach/pte/AbstractHafasProvider.java
index 2542ff2b..24efe9a8 100644
--- a/enabler/src/de/schildbach/pte/AbstractHafasProvider.java
+++ b/enabler/src/de/schildbach/pte/AbstractHafasProvider.java
@@ -1679,7 +1679,9 @@ public abstract class AbstractHafasProvider extends AbstractNetworkProvider
 				is.skipBytes(extensionHeaderPtr + 0x8);
 
 				final int seqNr = is.readShortReverse();
-				if (seqNr <= 0)
+				if (seqNr == 0)
+					throw new SessionExpiredException();
+				else if (seqNr < 0)
 					throw new IllegalStateException("illegal sequence number: " + seqNr);
 
 				final String requestId = strings.read(is);